Project Summary/Abstract Human immunodeficiency virus type 1 (HIV) infects brain macrophages and microglia and causes HIV- associated dementia (HAD), a primary disorder of the central nervous system (CNS) that affects about 20% of HIV-infected individuals. Current treatment of HAD is hampered by the poor efficiency of many antiretroviral drugs to cross the blood-brain barrier (BBB). Hence, new therapies for HAD are needed. Circulating blood monocyte-derived macrophages (MDM) are known to migrate across the BBB and to enter the CNS under both normal and certain circumstances; some subsequently maturing into long-lived tissue-resident brain macrophages and microglia. The hypothesis of this research is that it may be possible to exploit the natural homing/migratory properties of blood MDM in order to deliver neuroprotective factors into the CNS, in a non- invasive and non-surgical manner. Previous studies from our laboratory and others, have shown that MDM (human and mouse) can be genetically modified in vitro using defective lentiviral vectors (DLV) without adversely affecting their biological properties. Furthermore, we have shown that primary mouse blood monocytes and bone marrow-derived macrophages genetically modified by DLV can enter the brain, and that the efficiency of CNS uptake of these cells can be enhanced through transient disruption of the BBB. We have recently shown that secreted anti-HIV-Tat single chain antibodies (scFv) and soluble tumor necrosis factor receptor (sTNFR) from DLV-transduced MDM can effectively block the neurotoxic effects of conditioned medium from HIV-1 infected cells or respective recombinant proteins. In this project, we will establish a gene transfer method for high efficiency (>50%), stable transduction of primary mouse MDM with vectors that encode secretable scFv and sTNFR. We will then conduct studies to determine whether uptake of these genetically modified cells into the mouse brain can be enhanced using temporary disruption of the BBB, and we will evaluate the time course and stability of intra-CNS gene expression following peripheral infusion of the genetically-modified MDM. Finally, we will determine whether primary mouse MDM that stably express TNFR or anti-HIV-Tat scFv can ameliorate disease progression in two well-studied murine model systems for neuroAIDS. Successful completion of this study is expected to provide significant insight into new approaches for combating neuroAIDS and other neurologic disorders.